Drug-Resistance Gene Hopping Between Superbug Strains in New Delhi Water
Whatâ€™s the News: A gene that makes bacteria resistant to up to 14 antibiotics has been discovered in bacteria in drinking water and street puddles in the Indian capital of New Delhi by a research team from the University of Cardiff in Wales. Scientists were already aware that microbes bearing this gene, which produces an enzyme called NDM-1, were infecting people in India, but it had been thought that such bacteria were mainly picked up in hospitals. This study shows that the gene, which is capable of jumping from species to species, is loose in the environment.
Whatâ€™s the Context:
- NDM-1 is in a class of enzymes that are known culprits in the spread of drug-resistance: the beta-lactamases. The first beta-lactamase, penicillinase, was discovered in 1940 ($, pdf). These enzymes give resistance to antibiotics like cephamycins, carbapenems, and penicillin, which have similar chemical structures.
- The study is fueling fears that the NDM-1 gene could easily jump into bacteria around the world. Recently, a separate team of scientists showed that Swedish tourists returning from India had bacteria with beta-lactamases in their guts that they hadnâ€™t had before the trip. And as the current study found that the gene for NDM-1 skipped easily among bacterial species, the researchers are calling for greater action to fight drug-resistant bacteria in developing countries.
- Indian officials have spoken out against the study, in part over fears that it will damage Indiaâ€™s tourism industry. In an AP article, V.M. Katoch, director-general of the Indian Council of Medical Research, said, â€œWe know that such bacteria with genes are in the atmosphere everywhere. This is a waste of time. The study is creating a scare that India is a dangerous country to visit. We are condemning it.”
- This isnâ€™t the first time weâ€™ve heard of NDM-1: the gene has been on scientistsâ€™ radar since 2008, when it was first identified in a Swedish tourist returning from India. (For more background on the gene, see Scientific Americanâ€™s coverage.)
Not So Fast:
- The term â€œsuperbugâ€ has been racing from media outlet to media outlet. But this is a bit of a misnomer: this isnâ€™t a single new bacteria species endowed with phenomenal resistance, itâ€™s a gene that can bestow it.
- The difference is important. Dealing with a gene that can make any number of disease-causing bacteria resistant may be more difficult than focusing on just one species of bug—especially as the team found the gene in 20 types of bacteria, including those that cause dysentery and cholera. But the studyâ€™s findings suggest that the gene is much more likely to jump to new bacteria while outside the host (at temperatures typical of Indiaâ€™s climate, transfers were high; at body temperature, they dropped off). It would be interesting to see whether the fact that the gene needs lower temperatures to transfer could used to prevent its spread: if the transfer happens in drinking water, then better water treatment might help delay the formation of new resistant strains.
Reference: Toleman, M. et al. Dissemination of NDM-1 positive bacteria in the New Delhi environment and its implications for human health: an environmental point prevalence study. The Lancet Infectious Diseases, Early Online Publication, 7 April 2011. doi:10.1016/S1473-3099(11)70059-7
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